Volume control system



y 5, 1934. E. R. HENTSCHEL 1,958,999

VOLUME CONTROL SYSTEM Filed March 18, 1951 KLf E ff EEEIKK N) A TTORNEY Patented May 15, 1934 icE VOLUME CONTROL SYSTEM Ernest R. Hentschel, deceased, late of Springby John Olson, Springfield, Mm, assignor to administrator, Wired Radio, Inc.,

New York, N. Y., a corporation of Delaware.

Application March 18, 1931, Serial No. 523,569

4 Claims.

This invention relates broadly to radio broadcast receiving circuits and more particularly to a volume control system for radio broadcast receivers.

One of the objects of this invention is to pro vide a circuit arrangement for automatically controlling the efiective resistance of a portion of the amplification system of a radio receiver according to the volume of the reproduced sound.

Another object of this invention is to provide a circuit arrangement for a radio broadcast receiver in which an electron discharge path is included in circuit with the amplification system of a radio broadcast receiver and the effective resistance thereof controlled according to the volume of the reproduced sound for correspondingly controlling the amplification characteristics of the receiving apparatus.

Still another object of this invention is to provide a series circuit arrangement for the output circuit of a radio frequency amplifier and the circuit of an auxiliary control tube by which the effective resistance of the amplification system may be controlled in proportion to the volume of the reproduced sound for maintaining the reproduction of sound at substantially uniform volume.

Other and further objects of this invention reside in the circuit arrangement for a volume control system in a radio broadcast receiver as set forth more fully in the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates the volume control system of this invention applied to a standardized form of radio broadcast receiver.

Referring to the drawing in detail, the receiving apparatus includes a radio frequency amplifier constituted by electron tubes 1, 2 and 3, connected with the input'of a detector 4 whose output is connected through an audio frequency amplifier indicated in the drawing as constituted by a single amplification stage whose output circuit is connected to the loud speaker 35. The input circuit of the radio frequency amplifier connects'to the antenna ground circuit 36-3? which includes the primary winding 38 of a coupling' transformer whose secondary winding 39 is tuned by condenser 40 and connected across the input of the first stage of radio frequency amplification shown at 1. The output of the first radio frequency amplifier stage 1 is connected through coupling transformer 41 with the input circuit of electron tube 2, the input circuit being'tuned by means of condenser 42. The output circuit of electron tube 2 connects through transformer is with the input circuit of electron tube 3, the input circuit being tuned by means of condenser 44.. The output circuit of the radio frequency amplifier includes the primary windings of two radio frequency transformers in series. These transformers are designated at 45 and 46. The radio frequency transformer 45 has its secondary winding tuned by condenser 47 and connected to the input circuit of the electron tube detector 4. The output circuit of the detector l is coupled through audio frequency transformer 48 to the input of the audio frequency amplifier 5. An auxiliary detector tube 7 is connected to the secondary winding of the radio frequency transformer 46 as indicated at 9, the coupling circuit thus formed being tuned by condenser 49. A control tube 6 is provided having its output circuit connected in series with the output circuit of the radio frequency amplifier tube 1 in such manner that the effective resistance of the electron discharge path in the control tube 6 will control the effective potential'in the plate circuit of the radio. frequency amplifier tube 1. The power for energizing the several electron tubes is obtained from an alternating current power supply line to which is connected a suitable power transformer having primary windings 24 and a multiplicity of secondary windings. The secondary winding 23 is energized for heating the cathodes of the several electron tubes in thereceiver. One of the secondary windings connects to a full wave rectifier circuit designated at 22, the output from which connects to filter circuit 25 which in turn connects to the potentiometer 26. Taps are taken from the potentiometer 26 to the several plate, control grid and shield grid circuits of the tubes constituting the amplifier system. The tap 31 connects to the cathode return circuit common to all of the tubes. Tap 30 connects to the shield grid of the electron tube 1. Tap 32 connects to the grid circuits of tubes 1, 2 and 3. Tap 33 connects to the grid circuit of audio frequency amplifier 5. Tap 34 connects to the grid circuit of the detector tube 4. Tap 29 connects to the shield grid circuit of the electron tube detector 4. Tap 28 connects to the plate circuits of the radio frequency amplifier tubes 2 and 3. Tap 27 connects to the anode of the control tube 6 completing the output circuit of electron tube 1 through the cathode 50 in control tube 6 which connects to the high potential conductor 51 leading to the plate of the radio frequency amplifier tube 1. The tap connection 52 on potentiometer 26 connects to the plate circuit of the detector tube 4. The tap connection 53 on potentiometer 26 connects to the plate circuit of the amplifier tube 5. An auxiliary full wave rectifier circuit 21 is provided connecting with one of the windings of the power transformer in the power circuit to the receiver. The output of this auxiliary rectifier 21 connects through filter 20 to the potentiometer 16 from which taps are taken to control the bias potential on the control tube 6 and the auxiliary detector tube '7. The control tube 6 must have means for applying a negative bias to the grid so that the grid is made negative with respect to the oathode. It is impossible to use the main potential 26 for this purpose because the control :tube 6 is in series with the plate circuit of the radio frequency amplifier tube 1. It is for this reason that I provide the auxiliary rectifier 21 and the independent filter 20a and potentiometer 16. The auxiliary detector tube 7 connects through taps 1'7 and 18 on potentiometer :16 with the acircuits of the auxiliary detector tube as shown, the resistance 15 being interposed in series with such connection. The grid of control tube .6 connects through tap '54 with a point on resistance '15 as shown. The bias potential between the grid and cathode of the control tube '6 is therefore equal to the potential difference along resistance 15 which I have designated X added to the potential difference along potentiometer :16 designated Y, added to the potential difference along potentiometer 16 which I have designated Z. A filter system must be provided to eliminate both the audio frequency components and the radio frequency components from the auxiliary rectifier '7. The radio frequency filter elements are designated at '10 and 11 while the audio frequency :filter elements-are eliminated at .13 and '14.

In this method of volume control the current in tube 1 :is caused to vary by placing an additional tube :in :series in the plate circuit of tube 1. This additional tube does not carry radio frequency energy. Its resistance is varied by varying the grid bias. Choke coil 8 is placed in the circuit to prevent radio frequency energy from reaching the control tube 6. As the oathode of tube 6 must carry a high potential it cannot be connected to a common ground lead but is connected to a tap on resistance 16 as shown so that the path of the plate current of tube 1 is through choke 8, cathode to plate in tube 6 and then to tap 27 on potentiometer 26. The actuating energy for grid of tube 6 is supplied from the radio frequency plate circuit of tube 3 through coupling coil 9 and auxiliary detector 7 which is of the highly biased two-element type. When the radio frequency oscillations in the plate circuit of tube 3 exceed a certain predetermined value, current is passed from the oathode to the anode of tube '7, which also flows through portions of resistances 15 and 16. In order to obtain a bias on tube 7, I have shown an auxiliary rectifier 21 connected to the alternating current input. This rectifier supplies resistance 16 through filter 20. The bias on tube 7 is equal "to the potential between taps 1'? and 18 on resistance 16. There will be no current in resistance 15 at low amplitudes so therefore no correction needs to be made for any potential drop across resistance 15 but when energy exceeds the aforementioned predetermined value, current does flow in resistance 15 and the drop across this resistance and the portion of resistance 16 included between taps 1'7 and 19 is transferred to the grid of tube 6 to change the resistance of this tube to effect volume control. The portion of resistance 16 included between taps l7 and 19 places a steady bias on tube 6 by means of which the resistance of tube 6 can be adjusted to any desired value when no radio frequency energy is received. When radio frequency energy is received, the bias on tube 6 is equal to either the sum or difference of the potential drops across resistance 15 and the portion of resistance 16 aforementioned depending on whether tap 19 is to the right or left of connection 17. The connections can be so arranged that for very strong received signals the resistance of tube-6 can be made almost infinite.

The :sound reproduced at the loud speaker 35 is maintained at substantially uniform volume by the regulation offered by the auxiliary rectifier tube 7 with respect to the circuits of the control tube 6. Substantially uniform volume is maintained independent of fading effects or a tendency for the signaling energy to exceed a predetermined normal amplitude.

While this invention has been described .in one of its preferred embodiments, it is to be understood that modifications -may be made and that no limitations upon this invention are intended other than are imposed by the scope of the appended claims.

What is claimed as new and desired to secure by Letters Patent of the United States is as follows:

1. A volume control circuit for a radio broadcast receiver constituted by a radio frequency amplifier portion, a detector and an audio frequency amplifier portion having a sound reproducer connected therewith, an auxiliary detector connected to the output of said radio frequency amplifier portion, a control tube connected with the output of said auxiliary detector, said control tube including a cathode and an anode disposed in series with the output 'of one stage of amplification in said radio frequency amplifier portion, the connections between said control tube and :said auxiliary detector serving to adjust the effective resistance 'of the electron discharge path through said control tube and correspondingly-control the effective resistance of said radio frequency amplifier portion in accordance with the amplitude of the incoming signaling energy.

2. A volume control system for radio broadcast receivers including a radio frequency amplifier portion, a detector, an audio frequency amplifier portion and a loud speaker, an auxiliary detector, power supply means for the circuits of said radio broadcast receiver, a control tube disposed in series between said power supply means and part of said radio frequency amplifier portion, an independent energizing circuit interconnecting said power supply means with said auxiliary detector, and connections between said independent circuit and said control tube for modifying the operating characteristics thereof according to the amplitude of signaling energy incident upon said auxiliary detector for correspondingly controlling the effective resistance of said radio frequency amplifier and maintaining the reproduction of sound at said loud speaker substantially uniform.

3. A volume control system for radio broadcast receivers including a radio frequency amplifier portion, a detector, an audio frequency amplifier portion and a loud speaker, a power supply circuit for said radio broadcast receiver, a

control tube disposed in series between said power supply circuit and a portion of said radio frequency amplifier, an auxiliary detector and circuits controlled by the operation of said auxiliary detector for modifying the operation of said control tube for rendering the reproduction of sound at said loud speaker substantially uniform.

4. A volume control system for radio broadcast receivers including a radio frequency amplifier portion, a detector, an audio frequency amplifier portion and a loud speaker, a power supply circuit for said radio broadcast receiving apparatus, a control tube including an electron discharge path disposed in series between said power supply circuit and a portion of said radio frequency amplifier, an auxiliary detector and 

